The objectives of the proposed research are: 1. To understand adenovirus DNA replication. Replicating viral DNA will be isolated after short periods of radioactive labeling and separated by size. The newly-synthesized, small, viral DNA pieces will be hybridized with several isolated parts of the adenovirus genome (e.g., right and left halves) to determine the site from which these intermediates are replicated. 2. To determine the mechanism of action of camptothecin, a drug under clinical investigation as a therapeutic agent for human malignancy. We have previously shown that this compound nicks DNA. Its effects are reversible. The specificity of cleavage sites, the dependence on DNA replication and the requirement of protein synthesis for activity will be studied. 3> To define why adenovirus DNA replication is uniquely independent of continuous protein synthesis. This observation suggests that the proteins needed for replication of adenoviral DNA are unusually stable and, therefore, more easily studied. In addition, the apparent selectivity between cycloheximide inhibition of host but not viral DNA may offer an interesting model to study the control of viral DNA synthesis in transformed cells.